1. FIELD OF THE INVENTION
This invention relates to an easy and practical method for the removal of highly undesirable halogenated polycyclic compounds inevitably produced in the commercial production of halogenated phenols such as tetrachlorophenol and pentachlorophenol. More especially, this invention relates to the detoxification of residues obtained in the production of halogenated phenols by contacting substances containing the same with compounds containing carbon to carbon triple bonds.
2. DISCUSSION OF THE PRIOR ART
Of the more highly chlorinated phenols produced on a large technical scale by various methods, such as the chlorination of phenol or the hydrolysis of hexachlorobenzene, great importance has been acquired by tetrachlorophenol and pentachlorophenol and their derivatives. They are primarily fungistatic, but also have a bactericidal action, and they are used to a considerable extent in the building industry, in a variety of industrial processes and in agriculture, for example as wood protecting and preserving agents, as agents for the treatment of woods which can be attacked by microorganisms causing blue rot, as agents for combatting slime mold in the paper industry and other industries, and as harvesting aids, for example in the harvesting of cotton.
Under favorable conditions, impurities can be formed, some of which are toxic, from technical polychlorinated phenols. These impurities can be divided into four groups:
1. Chlorinated dibenzo-p-dioxins
2. Chlorinated dibenzofurans
3. Chlorinated hydroxydiphenylethers (predioxins and isopredioxins)
4. Chlorinated diphenylethers.
The toxicity of the first-named group of compounds is known; that of the other groups of compounds is considerably lower, but is not yet clearly understood.
The chlorinated dibenzo-p-dioxins, but also the substances of the third and fourth group are polychlorinated polycyclic aromatic or heteroaromatic substances which are extremely stable and very difficult to attack chemically. Attempts have been made to accelerate the decomposition of these substances by the action of ultraviolet light, in some cases with additional treatment with olive oil, but the effect and the rate of decomposition are poor.
A technically practicable method of rapidly destroying the above-named impurities has not been known hitherto.